Help test out ThinLTO!

From the current version of slab-alloc from cargo clean before each compilation:

Summary

Compilation difference: 2.5% slower

Runtime difference: 5.5% slower

Commands

(output trimmed)

$ time cargo test --release --no-run
real    1m30.323s
user    1m32.598s
sys     0m5.703s
$ time cargo test --release
real   0m8.650s
user   0m13.695s
sys    0m5.665s
$ RUSTFLAGS='-C codegen-units=16 -Z thinlto' time cargo test --release --no-run
real   1m32.65s
user   3m4.69s
sys    0m8.18s
$ RUSTFLAGS='-C codegen-units=16 -Z thinlto' time cargo test --release
real   0m9.15s
user   0m15.88s
sys    0m5.53s